Method of promoting the dispersion of solid particles in an electrolytic bath for composite electroplating of metals

ABSTRACT

In plating metals by composite or joint electrodeposition of, for example, nickel and silicon carbide particles thereon, sericite is added to the electrolytic bath to improve the dispersibility of the silicon carbide particles therein.

United States Patent Shigeru et al.

METHOD OF PROMOTING THE DISPERSION OF SOLID PARTICLES IN AN ELECTROLYTIC BATH FOR COMPOSITE ELECTROPLATING OF METALS Inventors: Ishimori Shigeru, Shizuoka Prefecture; Otsuka Shinjiro, Hamamatsu, both of Japan Assignee:

Filed:

App]. No.: 511,096

Foreign Application Priority Data O t 5 1973 J 48 112110 cles thereon, sericite is added to the electrolytic bath 6 to improve the dispersibility of the silicon carbide paru.s. Cl. 204/16; 204/49; 204/DIG. 2 cles Int. Cl. C23b 7/00; C23b 5/08 9 Claims, 4 Drawing Figures SEDIMENTATION VOLUME.

Suzuki Motor Company Limited, Shizuoka Prefecture, Japan Oct. 1, 1974 References Cited UNITED STATES PATENTS Primary Examiner-T. M. Tufariello Attorney, Agent, or Firm-Joseph P. Gastel [5 7] ABSTRACT CONTAINING NO SERICITE STANDING TIME. hr

[451 Sept. 9, 1975 [58] Field of Search 204/16, 49, DIG. 2, 45 R 3,061,525 10/1962 Grazen 204/16 3,644,183 2/1972 Odekerken 204/49 3,762,882 10/1973 Grutza 204/45 R l 1 1 CONTAINING lO SERICITE PATEN'IEDSEP ems 3,904,490

S'IIEET 1 [IF 2 CD g I I) CONTAINING Io SERICITE ui 8 E D l O 6 Z 9 E 4 g (ii) CONTAINING NO SERICITE 5 LL! (I) 2 I STANDING TIME. hr

NICKEL-SILICON CARBIDE COATING I5- I.O- m '0 1 NICKEL-SILICON CARBIDE-SERICITE COATING 3 0.5-

SILICON CARBIDE CONTENT. wI./

PATENTED SEP 9 9 5 PLATED COATING SHEET 2 OF 2 ARTICLE METHOD OF PROMOTING THE DISPERSION 0F SOLID PARTICLES IN AN ELECTROLYTIC BATH FOR COMPOSITE ELECTROPLATING OF METALS BACKGROUND OF THE INVENTION This invention relates generally to the art of electroplating, and in particular to the formation of plated coatings on metallic articles by composite or joint electrodeposition thereon ofa metal and finely divided particles of an insoluble solid in such a fashion that the solid particles are evenly dispersed throughout the bath and hence coatings. More specifically, the invention is directed to a method of promoting the formation and stabilization of a dispersion of the solid particles in an electrolytic bath containing a soluble compound of the metal.

As is well known. plated nickel coatings have silicon carbide particles dispersed therein, for example, have markedly improved wear resistance, so that the coatings of this character are being adopted advantageously for lining the cylinders of internal combustion engines, among other applications. For the formation of such composite plated coatings. it is the ordinary practice to cause the finely divided particles of silicon carbide to be dispersed in an electrolytic bath containing a soluble compound of nickel. An article to be plated is connected as the cathode in the bath, and the anode disposed in opposed relationship to the cathode is formed of nickel. Upon application of an electric current through the bath, nickel deposits on the article along with the silicon carbide particles.

In this composite electroplating operation according to the prior art, the silicon carbide particles must be held evenly dispersed in the bath in order to obtain plated coatings of unfluctuating quality. Heretofore, this requirement has been met by: (1) agitating the bath by mechanical means; (2) imparting vibratory motion to the article to be plated; or (3) introducing air bubbles into the bath through perforated pipes laid out at the bottom of the cell. All these conventional means are not entirely satisfactory because, upon cessation of their operation, the particles of silicon carbide and the like settle to the cell bottom in several hours. Preparatory to each run of electroplating operation. therefore, the bath must be sufficiently agitated to cause even dispersion of the solid particles therein. Time and labor conventionally expanded to this end has presented a serious bar to the increase in the productivity of the plating plant. It should also be taken into consideration that the listed mechanical means are relatively bulky and require unnecessarily large space for installation.

SUMMARY OF THE INVENTION.

In view of the noted state of the art.it is an object of this invention to provide. in the plating of metallic articles by composite or joint electrodeposition thereon of nickel and finely divided particles of an insoluble solid, a novel method of causing the even dispersion of the solid particles in the plated coatings by use of a high efficacious dispersant to be added to an electrolytic bath, whereby the need for provision of mechanical means for agitating the bath is substantially eliminated.

Another object of the invention is to provide a method of the character described wherein the dispersant in use is effective not only to cause the even dispersion of the solid particles but to improve the wearresistance. heat-resistance, hardness, lubricity, and other properties of the resulting plated coatings. whereby these coatings are made extremely suitable for surface protection of various metal-made articles including internal combustion engine cylinders.

With these objects in view and the other objects hereinafter set forth, this invention provides, in the art of plating metallic articles by joint electrodeposition of first and second components, wherein the first component is nickel and the second component a powder insoluble inv an electrolytic bath containing a soluble compound of nickel, an improved method which comprises adding sericite to the bath for promoting the formation and stabilization of a dispersion of the second component therein. Sericite is also effective in imparting wear resistance and lubricity to the plated coatings. Moreover, if, desired, sericite itself can be used as the second component.

The features which are believed to be novel and characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, as well as the further objects and advantages thereof, will become apparent from the following description including some specific examples to be taken in conjunction with the accompanying illustrations.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS In the illustrations:

FIG. I is agraph in which is plotted a curve (i) of the sedimentation volume in cubic centimeters per gram of silicon carbide particles (second component) in an electrolytic bath additionally containing a first component and a dispersant according to the invention against the standing time in hours of the bath and. by way of comparison, a curve (ii) of the sedimentation volume of silicon carbide particles in an electrolytic bath additionally containing the first component but no dispersant against the standing time of the bath;

FIG. 2 is a photomicrograph of a section of a coating plated on an iron casting by joint clectrodcposition thereon of nickel and sericite;

FIG. 3 is also a photomicrograph of a section of an other plated coating formed by joint electrodeposition of nickel, silicon carbide, and sericite; and

FIG. 4 is a graph indicating the results of wear tests ofa nickel-silicon carbide plated coating (indicated by the solid line) according to the prior art and ofa nickelsilicon carbide-scricite plated coating (dotted line) ac cording to the invention in relation to the silicon carbide contents of the coatings.

DETAILED DESCRIPTION The electrolytic bath for use in composite electro plating of metals according to the invention is composed of: (I) at least one first component selectable from compounds of nickel; (2) at least one second component selectable from oxides, carbides, metallic substances, ceramics, anad other inorganic substances in the form of insoluble powders; and (3) a dispersant for causing uniform dispersion of the second component in the bath and hence in electroplated coatingsv As the dispersant sericitc can be used.

While its properties and uses are well known in the art,- sericite may be described as a scaly variety of muscovite or white mica. Monoclinic in crystal system like muscovitc, sericite has a silky or pearly luster and imparts oilincss upon adhesion to the human skin. The crystalline grains of serieite are no more than about 2 microns in size. Sericite can also be described as a natural hydrous aluminum silicate, with a composition close to that of museovite, and has a low potassium content and a high moisture content. The general formula of serieite is:

it has now been discovered that the introduction of serieite or like dispersant into the bath containing the aforesaid first and second components materially retards the sedimentation velocity of the second compo nent. Furthermore, even after the second component has settled at the bottom of the cell with the elapse of time, the dispersant is effective in causing redispersion of the second component in the bath with significantly less physical effort than that required in accordance with the prior art.

Heretofore, the settlement of the second component at the cell bottom has easily taken place if the bath (not containing the dispersant according to the invention, of course) is allowed to stand for a few hours. if this second component is silicon carbide, and if its particles are about 3 microns or more in size, then these particles will coagulate in the bath. The expenditure of considerable physical effort, including the use of the listed mechanical means according to the prior art, is required to effect redispersion of the coagulated silicon carbide masses in the form of the initial sized particles.

The advantages resulting from the use of the dispersant according to this invention are manifested in the graph of FIG. 1. In this graph the curve (i) represents variation in silicon carbide sedimentation volume in cubic centimers per gram with the standing time in hours of a composite electroplating bath containing. in addition to the said first component, grams per liter of silicon carbide as the second component and I0 grams per liter of serieite as the dispersant. The curve (ii) in the same graph similarly represents variation in silicon carbide sedimentation volume in cubic centimcters per gram with the standing time in hours of a bath containing, in addition to the first component. 100 grams per liter of silicon carbide as the second component but no dispersant.

it will be apparent from a consideration of FIG. 1 that the use of serieite as the dispersant remarkably im proves the sedimentation characteristic of the second component in the solution of the first component. That is to say, the second component is made highly dispersible with respect to the first component. However. in order to ascertain the true advantage of the use of sericite as the dispersant in composite electroplating baths according to the invention, it will be necessary to examine the possibility of bath contamination as a result of its use.

An experiment was conducted to this end, in which serieite was first introduced into water in a quantity of 100 grams per liter. The mixture was stirred until the serieite became uniformly dispersed in the form of fine particles. This dispersion was then charged into a centrifugal separator of well known construction, and the machine was driven at a rate of 3,000 revolutions per minute for ID minutes. As a result of the atomic extinction analysis of the supernatant liquid thus obtained, 1 part per million of iron content, 8 parts per million of calcium content, 70 parts per million of sodium content, and 28 parts per million of potassium content were detected.

Of these metal contents, sodium and potassium are generally believed to affect the hardness of plated coatings when present as impurities in a nickel sulfamate bath. and iron and calcium to cause pittings and/or streaks. However, no such undesirable results are produced by serieite with such negligible metal contents. Since the pH of the composite electroplating bath according to the invention remains within the normal range after introduction of serieite therein, no repeated pH regulation is necessary. it has also been confirmed that serieite can impart lubricity and wear resistance to the plated coatings, so that this dispersant not only functions as such but shares the functions of the second component of the bath under consideration.

EXAMPLE I Composite nickel-serieite electroplating was conducted on sheet iron with a view to utilizing the lubricity and wear resistance possessed by serieite itself. A bath was prepared by using the solution of nickel sulfamate. Electrolytic nickel was used as the anode. The sheet iron to be plated was previously subjected to electrolytic alkali grease-removal treatment and acid treatment in accordance with the prior art. Various amounts of serieite were added to the bath, the added serieite ranging in the weight from about 5 to 100 grams per liter of the bath. The composition of the bath other than serieite and the plating condition are shown in Table 1. Generally, the viscosity of the bath increased with increase in the amount of serieite added, so that the bath required an increasingly greater degree of agitation by mechanical means. With the addition of more than 100 grams per liter of serieite, the bath could no longer be properly agitated. The coatings produced from such bath tended to exhibit stickiness and irregularity in thickness.

Anode Electrolytic Nickel EXAMPLE ll A bath having a composition shown in Table 1, Le. consisting of nickel sulfamate, nickel chloride, boric acid and sodium saccharin was admixed with grams per liter of serieite. With the use of this bath, an iron casting that had been subjected to the usual pretreat ment was electroplated under the same plating conditions as shown in Table l in a cell in accordance with the prior art process, in which the bath was constantly I agitated by blowing air under pressure from a compressor into perforated vinyl chloride pipes laid out at the bottom of the cell. The iron casting being plated was also subjected to constant vibratory motion. The process was carried out for 1 hours, with a current density of 20 amperes per square decimeter. The resultantly plated coating exhibited oiliness and smoothness obviously due to the addition of sericite to the bath.

A photomicrographie representation of a section of this composite electroplated coating is shown in FIG. 2. It will be clearly observed that the fine sericite particles are uniformly dispersed throughout the nickel layer on the iron casting. The average size of the sericite particles was found to be 0.3 microns.

It was also possible to plate similar articles with a current density of amperes per square decimeter and with sericite added to the bath in the range of from about 5 to 100 grams per liter. The resulting coatings equally exhibited oiliness and smoothness possessed by sericite. These properties were manifested even by the addition of a small amount of sericite to the bath.

The following Table 2 represents the results of chem ieal analyses of the various ingredients of the sericite used in the foregoing experiments. Table 3 shows the distribution of particle size of sericite used.

microns. Generally speaking, the sedimentation velocity of the silicon carbide particles increases with the increase in their size and with the decrease in the silicon carbide amount added to the bath. Also. the greater the size of the silicon carbide particles that have settled at the bottom of the cell. the more easily will they coagulate.

Table 4 below represents the relationship between the quantities in grams per liter of various sized silicon carbide particles to a nickel sulfamate bath and their sedimentation velocities in centimeters per hour. The bath has no sericite content. It should be noted in connection with this table that even when 150 grams per liter of silicon carbide particles with an average size of 2.2 microns is added to the bath. in which case the lowest sedimentation velocity is exhibited. the particles will coagulate if the bath is allowed to stand for several Table 2 lngredi- SiO A1 0 Fe O; FeO TiO CaO MgO K 0 cm Weight 47.21 .62 0.36 0.l 0.14 0.l 1.45 6.70 ratio, 7r

lngredi Na O lgnition Total ent loss Weight 0.76 9.49 101.93 ratio, /1

Table 3 Particle 2.0 1.0 0.8 0.6 0.4 0.2 Less than size. ;L 1.0 0.8 0.6 0.4 0.2 0.1 0.1

Weight 0.25 1.25 8.5 21.0 33.0 21.0 15.0 ratio. 7:

EXAMPLE 111 4 days to such an extent that they cannot be easily redis- As set forth in the preceding two Examples, sericite can be added to the bath in a quantity anywhere in the range of from about 5 to 100 grams per liter in the case of nickel-sericite plating. The upper limit becomes considerably lower in the case of nickel-silicon carbidesericite plating. This is because, upon introduction of silicon carbide to a nickel solution, the viscosity of the resultant dispersant naturally becomes significantly higher than that of the nickel solution. The amount of sericite to be added to the bath is therefore determined more or less by the amount of silicon carbide added.

It has been experimentally confirmed that, to a bath containing from 50 to 150 grams per liter of silicon carbide with a particle size of not more than about 8 microns. there can be added up to about grams per liter of sericite without causing any substantial flaws in the plated coatings. Should this upper limit be exceeded, the bath would become too viscous to be stirred properly, and the plated coatings would exhibit undue stickiness.

The principal advantage of adding sericite to nickelsilicon carbide baths is that the silicon carbide particles are thereby rendered highly dispe'rsible and are further prevented from coagulating. The particle size of silicon carbide is in the range of ll0 microns, preferably 2-4 persed by mechanical means.

Upon introduction of sericite to this nickelsilicon carbide bath. the silicon carbide particles become uniformly dispersed and become materially reduced in sedimentation velocity. The silicon carbide particles will not coagulate if the bath is allowed to stand for several days. This obviously is because. since the sericite particles added to the bath are as fine as about 0.3 microns in average size. the coarser silicon carbide particles are carried, so to say. by those of sericite and are thereby held dispersed in the bath. More specifically. upon introduction of 10 grams per liter of sericite to the nickel-silicon carbide baths represented in Table 4. the sedimentation velocities of the silicon carbide particles drop to about l/2.5 through [/23 of those exhibited in the case of no sericite introduction to the baths.

as evidenced by the. experimentally confirmed figures of the following Table 5:

Table 5 Si( Quantity added. g/l

Average 50 I lfil) Particle size. t

2.2 l cm/hr 1.1 cm/hr 1.5 cm/hr 3.7 L8 cm/hr l.7 cm/hr l em/hr It has also been experimentally confirmed that the sedimentation velocities of the various sized silicon carbide particles remain largely unchanged if sericite is added to the baths in quantities in excess of about 15 grams per liter. This relationship is given in Table 6 be-.

low, in which it is understood that the average size of the silicon carbide particles is 3.7 microns.

The electroplating operation was carried out with a current density of 20 amperes per square decimeter. The silicon carbide content of the electroplated coating was from about to 7 percent. FIG. 3 is the photomierographic representation of a ground cross section of the electroplated coating. fromwhich it will be noted that the silicon carbide particles are uniformly dispersed throughout the coating.

This coating is also notable for its improved heat re- Table 6 Sericite Quantity added. g/] 0 l0 SiC Quantity added. g/l

36.4 cm/hr 1.8 0.8 0.5 0.4 0.4 150 7 cm/hr 1.0 0.6 0.5 0.3 0.3

As previously stated. the bath viscosity increases with increase in the quantity of sericite added. tending to cause stickiness in the plated coatings. Generally, the viscosity of a liquid increases in substantial proportion with its content ofparticulatc matter. it is therefore appropriate for most practical purposes that no more than about 40 grams per liter of sericite be added to an electroplating bath with a large content of fine silicon carbide particles. Table 7 below rcpresent typical examples of the relationship between the amount in grams per liter of sericite added and the resulting viscosity ijn eentipoiscs of nickel baths each containing 100 grams per liter of different sized silicon carbide particles.

sistance. especially at about 300C. Tabulated below as Table 9 are the results of hardness testing of a coating electroplated from a nickel bath containing 100 grams per liter of silicon carbide only and of another coating electroplated from a nickel bath containing 100 grams per liter of silicon carbide and 20 grams per liter of sericitc. Prior to the hardness tests. the coating specimens were charged into an electric furnace which had been heated to the specified temperatures and were allowed to stand for 1 hour therein. The thus heated specimens were then allowed to cool in the atmosphere. and their hardness was then measured by means of a micro- Vickers hardness tester.

Table 9 Heat Treatment Temperature. C

No treatment 100 200 300 400 500 Coating Composition Nickel-Silicon 534 MHv 540 539 347 295 265 Carbide Nickel-Silicon 565 MHv 579 592 539 333 307 Carbidc-Sericite A nickel sulfamate electrolytic bath was prepared which additionally contained grams per liter of silicon carbide with an average particle size of 3.7 microns and 20 grams per liter of sericitc. The composition and the plating condition are the same as Table 8.

It can be said from these results of the heated coating specimens that the addition of sericite to the nickelsilicon carbide bath brings about no pronounced effect from no treatment up to about.200C of heating treatment. However, while the coatings with no sericite content exhibit a rapid drop in hardness at about 300C, those containing sericite according to this invention exhibit such a drop in hardness only at about 400C. It may be stated on the basis of Table 9 that the hardness of the coatings according to the invention after 400C heat treatment corresponds to that ofthe prior art coatings after 300C heat treatment, and that the hardness of the coatings according to the invention after 500C heat treatment corresponds to that of the prior art coatings after 400C heat treatment. Thus the addition of sericite to the composite electroplating bath is effective in improving the heat resistance of the coatings without causing any adverse effect on their hardness.

As an additional advantage, the surface of the coatings plated from the nickel-silicon carbide-sericite bath are just as smooth and oily as those of the coatings plated from the nickelsericite bath The anti-wear property of the former type of coating can thus be markedly improved as a result of the use of sericitc as the dispersant.

As set forth hereinbelow, there are numerous advantages resulting from the use of the nickel-silicon carbide-sericitc electroplating bath according to this invention. First of all, upon introduction of sericitc to a nickel sulfamate bath containing from about 50 to 150 grams per liter of silicon carbide, the silicon carbide particles become highly dispersible in the bath. Moreover, the silicon carbide particles become significantly reduced in sedimentation velocity and are further prevented from readily coagulating. It is therefore possible to correspondingly increase the content of silicon carbide or like second component in the plated coatings without causing irregularity in the dispersed state of the particles of the silicon carbide or the like in the coatings. The wear resistance of the plated coatings is thus markedly improved,

if the bath is allowed to stand for several days, no substantial coagulation of the silicon carbide particles takes places thanks to the presence of sericitc therein, so that the sedimcnted silicon carbide particles, if any, can easily be rcdispersed by mechanical means of any known or suitable type. Convcntionally, in a bath with no sericite content, the silicon carbide particles have easily coagulated if the bath is allowed to stand for a few days. Considerable time and labor has had to be expended to cause complete redispersion of the coagulated particles. Such expenditure of time and labor becomes substantially unnecessary by the addition of sericite to the bath. The desired results can be obtained even by the addition of about 10 grams per liter of sericite. However, in consideration of the actual plated coatings, up to about 40 grams per liter, and most appropriately about grams per liter, of sericite may ordinarily be employed.

The plated coatings formed by the addition of sericite to the nickel-silicon carbide bath have improved hardness at temperatures of about 300C or more. While the coatings plated in a bath with no sericite content according to the prior art suffer a marked drop in hardness in a temperature range of from about 200 to 300C, those plated in the bath containing sericite according to the invention exhibit a similar drop in hard ness only in a temperature range of from about 300 to 400C. The wear resistance of the coatings according to the invention is also materially improved due to the inherent lubricity of sericitc.

Table 10 Chemical Composition, Appearance Specific SiC Free Free Fe. .O,

Gravity Carbon Green powder 3,20 98.8 0.19 0.04

The composition of the bath and the conditions of the electroplating operation as employed in this Example was the same as Table 8 shown hereinbefore.

The aforementioned photomicrograph of FIG. 3 represents a section of the coating formed under the foregoing conditions.

In order to ascertain the variation in the quantity of siliconcarbide deposited along with nickel on articles to be plated with the quantity of sericite added to the bath, the sericitc content of the bath was varied to the various values set forth in Table 11 below, while the other conditions of the bath and plating operation were maintained exactly as specified in Table 10. As a result, it was found that the dispersibility of the silicon carbide particles in the bath improves with the increase in its sericite content, resulting in a corresponding increase in the amount of silicon carbide deposited on the articles together with nickel. In the series of experiments now under consideration, a coulometric carbon tester was employed to measure the carbon contents of the plated coatings by burning the same, and the silicon carbide contents of the coatings were computed on the bases of their carbon contents. The results were as follows.

Content of Plated Coating, wt. '71

The nickel-silicon carbide-sericite plated coatings according" to the invention and nickel-silicon carbide plated coatings according to the prior art were further subjected to Ohkoshi wear tests with the aim of determining the relationship between the wear resistance of the coatings and their silicon content. The wear resistance of the two types of coatings thus ascertained was also evaluated in relation to the use of scricite as the dispersant. The required variation in the silicon carbide content of the test specimens was caused by controlling the amount of silicon carbide introduced into the bath. Silicon carbide particles with an average size of 3.7 microns were used for the preparation of all the test specimens.

In the above mentioned Ohkoshi wear tests, a rotor in the form of an iron casting was driven under load in sliding contact with each coating specimen plated on a stator. Further details of these tests are given in Table 12 below.

Friction Mode Table 12 Dripping Mobil No. 20 Lubrication Oil at 40C Friction Velocity, 0.5!

m/sec Final Load, kg/cm l8!) Friction Distance, in 600 The test results are graphically represented in FIG. 4. It will be apparent from this graph that the wear resistance of the plated coatings is improved with increase in their silicon carbide contents. Greater improvement in wear resistance is exhibited as a result of the addition of sericite to the nickel-silicon carbide bath. Obviously, these results are attributable to the intrinsic lubricity of sericite and to the hardness of silicon carbide. It is therefore apparent that the use of sericite as the dispersant has a secondary effect of improving the wear resistance of the resulting plated coatings.

While in the explanation given above, silicon carbide is used as the insoluble powder of the second component, similar effect may also be achieved when powders of other inorganic substances which are insoluble to the electrolyte are used.

The second component and the dispersant are chemically independent, and the sedimentation speed of the second component is madeslower simply by a physical phenomenon. As for the parameters which has an immediate relation with the sedimentation speed, the differences between the specific gravities and the particle sizes of the second component and sericite. The specific weight of sericite itself is not so small (specific gravity 277-288), but the particle size is so small that the sedimentation speed becomes very small in the solution as compared with the second component. The

inherent property of sericite that it has a slow sedimentation speed, or in other words, an excellent dispersing property in the solution controls the sedimentation of the second component. it follows that the same effect may be expected for the second components other than ing hereof, which modifictions will, not constitute departures from the spirit and scope of the invention.

What is claimed is:

1. In a method of plating metallic articles by composite electro-deposition thereon of first and second components, wherein said first component is nickel and said second component a powder insoluble in an electrolytic bath containing at least a soluble compound of nickel, the improvement which comprises adding sericite to the electrolytic bath as a dispersant of said second component with respect to said first component.

2. In a method of plating metallic articles by composite electrodeposition thereon of first and second com ponents, wherein said first component is nickel and said second component a powder insoluble in an electrolytic bath containing at least a soluble compound of nickel, the improvement which comprises adding sericite to the electrolytic bath as said second component.

3. The improvement as set forth in claim 1 wherein the amount of sericite added to the electrolytic bath is in the range of from about 5 to about grams per liter of the bath.

4. The improvement as set forth in claim 2 wherein the amount of sericite added to the electrolytic bath is in the range of from about 5 to about 100 grams per liter of the bath.

5. The improvement as set forth in claim 1 wherein said second component is a member selected from the group consisting of insoluble powders of oxides, carbides, metallic substances, and ceramics, said bath containing at least a soluble compound of said first component and said second component.

6. The improvement as set forth in claim 1 wherein said second component is silicon carbide in particulate form.

7. The improvement as set forth in claim 6 wherein the amount of silicon carbide contained in the electrolytic bath is in the range of from about 50 to about grams per liter of the bath exclusive of the sericite content thereof.

8. The improvement as set forth in claim 6 wherein the particle size of silicon carbide contained in the electrolytic bath is in the range of from 1 micron to 10 microns.

9. The improvement as set forth in claim 7 wherein the particle size of silicon carbide contained in the electrolytic bath is in the range of from 1 micron to 10 mi- CTOHS- 

1. IN A METHOD OF PLATING METALLIC ARTICLES BY COMPOSITE ELECTRO-DEPOSITION THEREON OF FIRST AND SECOND COMPOSITE WHEREIN SAID FIRST COMPONENT IS NICKEL AND SAID SECOND COMPONENT A POWDER INSOLUBLE IN AN ELECTROLYTIC BATH CONTAING AT LEAST A SOLUBLE COMPOUND OF NICKEL, THE IMPROVEMENT WHICH COMPRISES ADDING SERICITE TO THE ELECTROLYTIC BATH AS A DISPERSANT OF SAID SECOND COMPONENT WITH RESPECT TO SAID FIRST COMPONENT.
 2. In a method of plating metallic articles by composite electrodeposition thereon of first and second components, wherein said first component is nickel and said second component a powder insoluble in an electrolytic bath containing at least a soluble compound of nickel, the improvement which comprises adding sericite to the electrolytic bath as said second component.
 3. The improvement as set forth in claim 1 wherein the amount of sericite added to the electrolytic bath is in the range of from about 5 to about 100 grams per liter of the bath.
 4. The improvement as set forth in claim 2 wherein the amount of sericite added to the electrolytic bath is in the range of from about 5 to about 100 grams per liter of the bath.
 5. The improvement as set forth in claim 1 wherein said second component is a member selected from the group consisting of insoluble powders of oxides, carbides, metallic substances, and ceramics, said bath containing at least a soluble compound of said first component and said second component.
 6. The improvement as set forth in claim 1 wherein said second component is silicon carbide in particulate form.
 7. The improvement as set forth in claim 6 wherein the amount of silicon carbide contained in the electrolytic bath is in the range of from about 50 to about 150 grams per liter of the bath exclusive of the sericite content thereof.
 8. The improvement as set forth in claim 6 wherein the particle size of silicon carbide contained in the electrolytic batH is in the range of from 1 micron to 10 microns.
 9. The improvement as set forth in claim 7 wherein the particle size of silicon carbide contained in the electrolytic bath is in the range of from 1 micron to 10 microns. 